don't list webapps on user profile (bug 1015378)

Fixes [bug 1015378](https://bugzilla.mozilla.org/show_bug.cgi?id=1015378)

This is a temporary fix that we'll be able to remove when bug
https://bugzilla.mozilla.org/show_bug.cgi?id=1020465 lands (it removes the
zamboni related data and files).